The long-term objective of the proposed research is to understand the physiology and pharmacology of the neural systems that transmit and modulate pain. The specific aim of these studies is to determine the electrical properties of isolated spinothalamic tract cells and the mode of action of a number of transmitter substances on these cells. The objectives of these experiments are (1) to determine the voltage dependent properties of identified spinothalamic cells and (2) to characterize the actions and interactions of peptides and biogenic amines on these cells. The ionic current of identified single STT cells will be measured under voltage clamp conditions. Patch pipette voltage clamp technique will be used. The fundamental knowledge obtained from these experiments will be essential in defining the mechanisms of action of the putative transmitter in spinothalamic cells.